Browsing by Subject "disk galaxies"

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Barred Galaxies In The Abell 901/2 Supercluster With Stages
(2009-06) Marinova, Irina; Jogee, Shardha; Heiderman, Amanda; Barazza, Fabio D.; Gray, M. E.; Barden, Marco; Wolf, Christian; Peng, Chen Y.; Bacon, David; Balogh, Michael; Bell, Eric F.; Bohm, Asmus; Caldwell, John A. R.; Haussler, Boris; Heymans, Catherine; Jahnke, Knud; van Kampen, Eelco; Lane, Kyle; McIntosh, Daniel H.; Meisenheimer, Klaus; Sanchez, Sebastian F.; Somerville, Rachel; Taylor, Andy; Wisotzki, Lutz; Zheng, Xianzhong; Marinova, Irina; Jogee, Shardha; Heiderman, Amanda
We present a study of bar and host disk evolution in a dense cluster environment, based on a sample of similar to 800 bright (M-V <= -18) galaxies in the Abell 901/2 supercluster at z similar to 0.165. We use Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) F606W imaging from the STAGES survey, and data from Spitzer, XMM-Newton, and COMBO-17. We identify and characterize bars through ellipse-fitting, and other morphological features through visual classification. We find the following results. (1) To define the optical fraction of barred disk galaxies, we explore three commonly used methods for selecting disk galaxies. We find 625, 485, and 353 disk galaxies, respectively, via visual classification, a single component Sersic cut (n <= 2.5), and a blue-cloud cut. In cluster environments, the latter two methods suffer from serious limitations, and miss 31% and 51%, respectively, of visually identified disks, particularly the many red, bulge-dominated disk galaxies in clusters. (2) For moderately inclined disks, the three methods of disk selection, however, yield a similar global optical bar fraction (f(bar-opt)) of 34%(+10%)(-3%) (115/340), 31%(+10%)(-3%) (58/189), and 30%(+10%)(-3%) (72/241), respectively. (3) We explore f(bar-opt) as a function of host galaxy properties and find that it rises in brighter galaxies and those which appear to have no significant bulge component. Within a given absolute magnitude bin, f(bar-opt) is higher in visually selected disk galaxies that have no bulge as opposed to those with bulges. Conversely, for a given visual morphological class, f(bar-opt) rises at higher luminosities. Both results are similar to trends found in the field. (4) For bright early-types, as well as faint late-type systems with no evident bulge, the optical bar fraction in the Abell 901/2 clusters is comparable within a factor of 1.1-1.4 to that of field galaxies at lower redshifts (z < 0.04). (5) Between the core and the virial radius of the cluster (R similar to 0.25-1.2 Mpc) at intermediate environmental densities (log(Sigma(10)) similar to 1.7-2.3), the optical bar fraction does not appear to depend strongly on the local environment density tracers (kappa, Sigma(10), and intracluster medium (ICM) density), and varies at most by a factor of similar to 1.3. Inside the cluster core, we are limited by number statistics, projection effects, and different trends from different indicators, but overall f(bar-opt) does not show evidence for a variation larger than a factor of 1.5. We discuss the implications of our results for the evolution of bars and disks in dense environments.
Bulge n And B/T In High-Mass Galaxies: Constraints On The Origin Of Bulges In Hierarchical Models
(2009-05) Weinzirl, Tim; Jogee, Shardha; Khochfar, S.; Burkert, Andreas; Kormendy, John; Weinzirl, Tim; Jogee, Shardha; Kormendy, John
We use the bulge Sersic index n and bulge-to-total mass ratio (B/T) to explore the fundamental question of how bulges form. We perform two-dimensional bulge-disk-bar decomposition on H-band images of 143 bright, high-mass (M(*) >= 1.0 x 10(10) M(circle dot)) low-to-moderately inclined (i < 70 degrees) spirals. Our results are as follows. (1) Our H-band bar fraction (similar to 58%) is consistent with that from ellipse fits. (2) 70% of the stellar mass is in disks, 10% in bars, and 20% in bulges. (3) A large fraction (similar to 69%) of bright spirals have B/T <= 0.2, and similar to 76% have low n <= 2 bulges. These bulges exist in barred and unbarred galaxies across a wide range of Hubble types. (4) About 65% (68%) of bright spirals with n <= 2 (B/T <= 0.2) bulges host bars, suggesting a possible link between bars and bulges. (5) We compare the results with predictions from a set of ACDM models. In the models, a high-mass spiral can have a bulge with a present-day low B/T <= 0.2 only if it did not undergo a major merger since z <= 2. The predicted fraction (similar to 1.6%) of high-mass spirals, which have undergone a major merger since z <= 4 and host a bulge with a present-day low B/T <= 0.2, is a factor of over 30 smaller than the observed fraction (similar to 66%) of high-mass spirals with B/T <= 0.2. Thus, contrary to common perception, bulges built via major mergers since z <= 4 seriously fail to account for the bulges present in similar to 66% of high mass spirals. Most of these present-day low B/T <= 0.2 bulges are likely to have been built by a combination of minor mergers and/or secular processes since z <= 4.
Bulges Of Nearby Galaxies With Spitzer: Scaling Relations In Pseudobulges And Classical Bulges
(2010-06) Fisher, David B.; Drory, Niv; Fisher, David B.
We investigate scaling relations of bulges using bulge-disk decompositions at 3.6 mu m and present bulge classifications for 173 E-Sd galaxies within 20 Mpc. Pseudobulges and classical bulges are identified using Sersic index, Hubble Space Telescope morphology, and star formation activity ( traced by 8 mu m emission). In the near-IR pseudobulges have n(b) < 2 and classical bulges have n(b) > 2, as found in the optical. Sersic index and morphology are essentially equivalent properties for bulge classification purposes. We confirm, using a much more robust sample, that the Sersic index of pseudobulges is uncorrelated with other bulge structural properties, unlike for classical bulges and elliptical galaxies. Also, the half-light radius of pseudobulges is not correlated with any other bulge property. We also find a new correlation between surface brightness and pseudobulge luminosity; pseudobulges become more luminous as they become more dense. Classical bulges follow the well-known scaling relations between surface brightness, luminosity, and half-light radius that are established by elliptical galaxies. We show that those pseudobulges (as indicated by Sersic index and nuclear morphology) that have low specific star formation rates are very similar to models of galaxies in which both a pseudobulge and classical bulge exist. Therefore, pseudobulge identification that relies only on structural indicators is incomplete. Our results, especially those on scaling relations, imply that pseudobulges are very different types of objects than elliptical galaxies.
Detection of A Pseudobulge Hidden inside the "Box-Shaped Bulge" of NGC 4565
(2010-06) Kormendy, John; Barentine, John C.; Kormendy, John; Barentine, John C.
Numerical simulations show that box-shaped bulges of edge-on galaxies are not bulges: they are bars seen side-on. Therefore, the two components that are seen in edge-on Sb galaxies such as NGC 4565 are a disk and a bar. But face-on SBb galaxies always show a disk, a bar, and a (pseudo) bulge. Where is the (pseudo) bulge in NGC 4565? We use archival Hubble Space Telescope H-band images and Spitzer Space Telescope 3.6 mu m wavelength images, both calibrated to Two Micron All Sky Survey K(s) band, to penetrate the prominent dust lane in NGC 4565. We find a high surface brightness, central stellar component that is clearly distinct from the boxy bar and from the disk. Its brightness profile is a Sersic function with index n = 1.55 +/- 0.07 along the major axis and 1.33 +/- 0.12 along the minor axis. Therefore, it is a pseudobulge. It is much less luminous than the boxy bar, so the true pseudobulge-to-total luminosity ratio of the galaxy is PB/T = 0.06 +/- 0.01, much less than the previously believed value of B/T = 0.4 for the "boxy bulge." We infer that published B/T luminosity ratios of edge-on galaxies with boxy bulges have been overestimated. Therefore, more galaxies than we thought contain little or no evidence of a merger-built classical bulge. From a Formation point of view, NGC 4565 is a giant, pure-disk galaxy. This presents a challenge to our picture of galaxy Formation by hierarchical clustering: it is difficult to grow galaxies as big as NGC 4565 without also making big classical bulges.
Frequency And Properties Of Bars In Cluster And Field Galaxies At Intermediate Redshifts
(2009-04) Barazza, F. D.; Jablonka, P.; Desai, V.; Jogee, S.; Aragon-Salamanca, A.; De Lucia, G.; Saglia, R. P.; Halliday, C.; Poggianti, B. M.; Dalcanton, J. J.; Rudnick, G.; Milvang-Jensen, B.; Noll, S.; Simard, L.; Clowe, D. I.; Pello, R.; White, S. D. M.; Zaritsky, D.; Jogee, S.
We present a study of large-scale bars in field and cluster environments out to redshifts of similar to 0.8 using a final sample of 945 moderately inclined disk galaxies drawn from the EDisCS project. We characterize bars and their host galaxies and look for relations between the presence of a bar and the properties of the underlying disk. We investigate whether the fraction and properties of bars in clusters are different from their counterparts in the field. The properties of bars and disks are determined by ellipse fits to the surface brightness distribution of the galaxies using HST/ACS images in the F814W filter. The bar identification is based on quantitative criteria after highly inclined (> 60 degrees) systems have been excluded. The total optical bar fraction in the redshift range z = 0.4-0.8 (median z = 0.60), averaged over the entire sample, is 25% (20% for strong bars). For the cluster and field subsamples, we measure bar fractions of 24% and 29%, respectively. We find that bars in clusters are on average longer than in the field and preferentially found close to the cluster center, where the bar fraction is somewhat higher (similar to 31%) than at larger distances (similar to 18%). These findings however rely on a relatively small subsample and might be affected by small number statistics. In agreement with local studies, we find that disk-dominated galaxies have a higher optical bar fraction (similar to 45%) than bulge-dominated galaxies (similar to 15%). This result is based on Hubble types and effective radii and does not change with redshift. The latter finding implies that bar formation or dissolution is strongly connected to the emergence of the morphological structure of a disk and is typically accompanied by a transition in the Hubble type. The question whether internal or external factors are more important for bar formation and evolution cannot be answered definitely. On the one hand, the bar fraction and properties of cluster and field samples of disk galaxies are quite similar, indicating that internal processes are crucial for bar formation. On the other hand, we find evidence that cluster centers are favorable locations for bars, which suggests that the internal processes responsible for bar growth are supported by the typical interactions taking place in such environments.
GEMS : Galaxy Fitting Catalogs and Testing Parametric Galaxy Fitting Codes : GALFIT and GIM2D
(2007-10) Haeussler, Boris; McIntosh, Daniel H.; Barden, Marco; Bell, Eric F.; Rix, Hans-Walter; Borch, Andrea; Beckwith, Steven V. W.; Caldwell, John A. R.; Heymans, Catherine; Jahnke, Knud; Jogee, Shardha; Koposov, Sergey E.; Meisenheimer, Klaus; Sanchez, Sebastian F.; Somerville, Rachel S.; Wisotzki, Lutz; Wolf, Christian; Caldwell, John A. R.
In the context of measuring the structures of intermediate-redshift galaxies with HST ACS surveys, we tune, test, and compare two widely used fitting codes (GALFIT and GIM2D) for fitting single-component Sersic models to both simulated and real galaxy data. Our study focuses on the GEMS survey with the sensitivity of typical HST survey data, and we include our final catalog of fit results for all 41,495 objects detected in GEMS. Using simulations, we find that fitting accuracy depends sensitively on galaxy profile shape. Exponential disks are well fit and have small measurement errors, whereas fits to de Vaucouleurs profiles show larger uncertainties owing to the large amount of light at large radii. Both codes provide reliable fits with little systematic error for galaxies with effective surface brightnesses brighter than that of the sky; the formal uncertainties returned by these codes significantly underestimate the true uncertainties (as estimated using the simulations). We find that GIM2D suffers significant systematic errors for spheroids with close companions owing to the difficulty of effectively masking out neighboring galaxy light; there appears to be no work-around to this important systematic in GIM2D's current implementation. While this crowding error affects only a small fraction of galaxies in GEMS, it must be accounted for in the analysis of deeper cosmological images or of more crowded fields with GIM2D. In contrast, GALFIT results are robust to the presence of neighbors because it can simultaneously fit the profiles of multiple companions as well as the galaxy of interest. We find GALFIT's robustness to nearby companions and factor of greater than or similar to 20 faster runtime speed are important advantages over GIM2D for analyzing large HST ACS data sets.
Kinematics At the Edge of the Galactic Bulge: Evidence for Cylindrical Rotation
(2009-09) Howard, Christian D.; Rich, R. Michael; Clarkson, Will; Mallery, Ryan; Kormendy, John; De Propris, Roberto; Robin, Anne C.; Fux, Roger; Reitzel, David B.; Zhao, HongSheng; Kuijken, Konrad; Koch, Andreas; Kormendy, John
We present new results from BRAVA, a large-scale radial velocity survey of the Galactic bulge, using M giant stars selected from the Two Micron All Sky Survey catalog as targets for the Cerro Tololo Inter-American Observatory 4 m Hydra multi-object spectrograph. The purpose of this survey is to construct a new generation of self-consistent bar models that conform to these observations. We report the dynamics for fields at the edge of the Galactic bulge at latitudes b = -8 degrees and compare to the dynamics at b = -4 degrees. We find that the rotation curve V (r) is the same at b = -8 degrees as at b = -4 degrees. That is, the Galactic boxy bulge rotates cylindrically, as do boxy bulges of other galaxies. The summed line-of-sight velocity distribution at b = -8 degrees is Gaussian, and the binned longitude-velocity plot shows no evidence for either a (disk) population with cold dynamics or for a (classical bulge) population with hot dynamics. The observed kinematics are well modeled by an edge-on N-body bar, in agreement with published structural evidence. Our kinematic observations indicate that the Galactic bulge is a prototypical product of secular evolution in galaxy disks, in contrast with stellar population results that are most easily understood if major mergers were the dominant Formation process.
Observable Properties Of Double-Barred Galaxies In N-Body Simulations
(2009-01) Shen, Juntai T.; Debattista, Victor P.; Shen, Juntai T.
Although at least one quarter of early-type barred galaxies host secondary stellar bars embedded in their large-scale primary counterparts, the dynamics of such double-barred galaxies are still not well understood. Recently we reported success at simulating such systems in a repeatable way in collisionless systems. In order to further our understanding of double-barred galaxies, here we characterize the density and kinematics of the N-body simulations of these galaxies. This will facilitate comparison with observations and lead to a better understanding of the observed double-barred galaxies. We find the shape and size of our simulated secondary bars are quite reasonable compared to the observed ones. We demonstrate that an authentic decoupled secondary bar may produce only a weak twist of the kinematic minor axis in the stellar velocity field, due to the relatively large random motion of stars in the central region. We also find that the edge-on nuclear bars are probably not related to boxy peanut-shaped bulges which are most likely to be edge-on primary large-scale bars. Another kinematic feature often present in our double-barred models is a ring-like feature in the fourth-order Gauss-Hermite moment h(4) maps. Finally, we demonstrate that the non-rigid rotation of the secondary bar causes its pattern speed to not be derived with great accuracy using the Tremaine-Weinberg method. We also compare with observations of NGC 2950, a prototypical double-barred early-type galaxy, which suggest that the nuclear bar may be rotating in the opposite sense as the primary.
Physical And Morphological Properties Of O II Emitting Galaxies In The HETDEX Pilot Survey
(2015-02) Bridge, Joanna S.; Gronwall, Caryl; Ciardullo, Robin; Hagen, Alex; Zeimann, Greg; Malz, A. I.; Acquaviva, Viviana; Schneider, Donald P.; Drory, Niv; Gebhardt, Karl; Jogee, Shardha; Drory, Niv; Gebhardt, Karl; Jogee, Shardha
The Hobby-Eberly Dark Energy Experiment pilot survey identified 284 [O II] lambda 3727 emitting galaxies in a 169 arcmin(2) field of sky in the redshift range 0 < z < 0.57. This line flux limited sample provides a bridge between studies in the local universe and higher-redshift [O II] surveys. We present an analysis of the star formation rates (SFRs) of these galaxies as a function of stellar mass as determined via spectral energy distribution fitting. The [O II] emitters fall on the "main sequence" of star-forming galaxies with SFR decreasing at lower masses and redshifts. However, the slope of our relation is flatter than that found for most other samples, a result of the metallicity dependence of the [O II] star formation rate indicator. The mass-specific SFR is higher for lower mass objects, supporting the idea that massive galaxies formed more quickly and efficiently than their lower mass counterparts. This is confirmed by the fact that the equivalent widths of the [O II] emission lines trend smaller with larger stellar mass. Examination of the morphologies of the [O II] emitters reveals that their star formation is not a result of mergers, and the galaxies' half-light radii do not indicate evolution of physical sizes.
A Quintet Of Black Hole Mass Determinations
(2009-04) Gueltekin, Kayhan; Richstone, Douglas O.; Gebhardt, Karl; Lauer, Tod R.; Pinkney, Jason; Aller, Monique C.; Bender, Ralf; Dressler, Alan; Faber, S. M.; Filippenko, Alexei V.; Green, Richard; Ho, Luis C.; Kormendy, John; Siopis, Christos; Gebhardt, Karl; Kormendy, John
We report five new measurements of central black hole masses based on Space Telescope Imaging Spectrograph and Wide Field Planetary Camera 2 observations with the Hubble Space Telescope (HST) and on axisymmetric, three-integral, Schwarzschild orbit-library kinematic models. We selected a sample of galaxies within a narrow range in velocity dispersion that cover a range of galaxy parameters (including Hubble type and core/power-law surface density profile) where we expected to be able to resolve the galaxy's sphere of influence based on the predicted value of the black hole mass from the M-sigma relation. We find masses for the following galaxies: NGC3585, M(BH) = 3.4(-0.6)(+1.5) x 10(8) M(circle dot;) NGC 3607, M(BH) = 1.2(-0.4)(+0.4) x 10(8) M(circle dot); NGC 4026, M(BH) = 2.1(-0.4)(+0.7) x 10(8) M(circle dot); and NGC 5576, M(BH) = 1.8(-0.4)(+0.3) x 10(8) M(circle dot), all significantly excluding M(BH) = 0. For NGC 3945, M(BH) = 9(-21)(+17) x 10(6) M(circle dot), which is significantly below predictions from M-sigma and M-L relations and consistent with MBH = 0, though the presence of a double bar in this galaxy may present problems for our axisymmetric code.
Two Pseudobulges In The "Boxy Bulge" Galaxy NGC 5746
(2012-08) Barentine, John C.; Kormendy, John; Barentine, John C.; Kormendy, John
Galaxy formation and growth under the Lambda CDM paradigm is expected to proceed in a hierarchical, bottom-up fashion by which small galaxies grow into large galaxies; this mechanism leaves behind large "classical bulges" kinematically distinct from "pseudobulges" grown by internal, secular processes. We use archival data (Spitzer Space Telescope 3.6 mu m wavelength, Hubble Space Telescope H-band, Two Micron All Sky Survey K-s-band, and Sloan Digital Sky Survey gri-band) to measure composite minor-and major-axis surface brightness profiles of the almost-edge-on spiral galaxy NGC 5746. These light profiles span a large range of radii and surface brightnesses to reveal an inner, high surface brightness stellar component that is distinct from the well-known boxy bulge. It is well fitted by Sersic functions with indices n = 0.99 +/- 0.08 and 1.17 +/- 0.24 along the minor and major axes, respectively. Since n < 2, we conclude that this innermost component is a secularly evolved pseudobulge that is distinct from the boxy pseudobulge. This inner pseudobulge makes up 0.136 +/- 0.019 of the total light of the galaxy. It is therefore considerably less luminous than the boxy structure, which is now understood to be a bar seen nearly end-on. The infrared imagery shows further evidence for secular evolution in the form of a bright inner ring of inner radius 9.1 kpc and width 1.6 kpc. NGC 5746 is therefore a giant, pure-disk SB(r) bc galaxy with no sign of a merger-built bulge. We do not understand how such galaxies form in a Lambda DM universe.